Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, and various signal processing circuits.
Semiconductor devices perform a wide range of functions such as signal processing, high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual images for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The structure of semiconductor material allows the material's electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed operations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, i.e., front-end manufacturing, and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of die on the surface of a semiconductor wafer. Each semiconductor die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual semiconductor die from the finished wafer and packaging the die to provide structural support, electrical interconnect, and environmental isolation. The term “semiconductor die” as used herein refers to both the singular and plural form of the words, and accordingly, can refer to both a single semiconductor device and multiple semiconductor devices.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and can be produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller semiconductor die size can be achieved by improvements in the front-end process resulting in semiconductor die with smaller, higher density active and passive components. Back-end processes may result in semiconductor device packages with a smaller footprint by improvements in electrical interconnection and packaging materials.
Wafer level chip scale package (WLCSP) and fan-out wafer level package (FO-WLP) often contain large array semiconductor die that redistribute signal paths from fine pitch bonding pads of the die to the periphery fan-out area for higher functional integration to external devices. The large array WLCSP are known to experience reliability problems, in particular with solder joint failures during temperature cycling and drop impact testing. In addition, the large array WLCSPs tend to have a warpage issue due to the large die size.
Another goal of semiconductor manufacturing is to produce higher performance semiconductor devices. An increase in device performance can be accomplished by forming active components that are capable of operating at higher speeds or frequencies. High-performance semiconductor devices generate significant heat that must be adequately dissipated. Without effective heat dissipation, the generated heat can reduce performance, decrease reliability, and reduce the useful lifetime of the semiconductor device. Conventional heat spreaders have too high of coefficients of thermal expansion (CTE), i.e., greater than 14 parts per million per degree Celsius (ppm/° C.). The semiconductor package is subject to warpage or bending due to differences in CTE of the semiconductor die and surrounding structures within the package, such as high CTE heat spreaders. Warpage of the semiconductor package can cause joint defects or failures and reduce reliability of the electrical connections across the device. Warpage of the semiconductor package also reduces manufacturing yield and package reliability, and leads to increased cost. Other heat spreaders have too low of thermal conductivity, i.e., less than 60 watts per meter kelvin (W/m·K), and lack adequate heat dissipation. Alternative materials used in heat spreaders, such as tungsten copper (WCu), molybdenum copper (MoCu), and MoCu alloys significantly increase the cost of manufacturing the semiconductor package.